This invention relates to devices for blending materials and bags for use in such devices. The materials to be mixed or blended may be liquids or semi-liquid matter, and in some cases solids, powders or even gases. The invention is particularly concerned with the preparation of samples for bacteriological or chemical testing.
There are existing blending devices comprising a door which acts as a support for holding a sample bag and two reciprocating paddles for acting on the bag. A bag may be placed on the support and then brought into an operating position (by closing the door of the device) to clamp in position and seal the bag. The paddles are arranged to reciprocate, alternately pressing on the outer surface of the bag, kneading the contents of the bag to achieve a blending action. The paddles reciprocate over a fixed range of motion and the support can be positioned so that there is always an appropriate gap in which the bag may sit during blending. The minimum gap between the paddles and the support during blending can be termed the “paddle clearance”.
During the time that blending devices of the type described above have been on the market, techniques for analyzing samples in the fields of bacteriological and chemical testing have improved. As a result of these improvements scientists now often work with smaller samples.
In general, when working with smaller samples, a smaller paddle clearance is required. Otherwise, the paddles either fail to make contact with the bag or make insufficient contact to achieve effective blending of the contents of the bag. The result of this is that smaller samples may remain unblended.
When working with smaller samples there is also a problem in obtaining a useful blended sample. For example, a conventional bag sold for use with a blending device marketed by the applicants is designed to hold between 5 ml and 80 ml of liquids—with such sized samples, good results are achieved. However, it has been found that if 250 μl of liquid is used in this conventional bag, the result can be that you merely end up with the inside of the bag becoming wet. It can be difficult or impossible to extract a useful sample of the liquid.
It is an object of the present invention to alleviate at least some of the problems associated with the prior art.
According to a first aspect of the present invention there is provided a device for blending materials comprising a carrier support arranged to support a closed bag containing material to be blended, at least one reciprocating kneading paddle having an extended position and being arranged to apply a kneading action to the walls of a supported bag for homogenizing its contents, and adjustment means for controllably varying a spacing between the paddle when in its extended position and the carrier support.
Such an arrangement can facilitate the blending of differently sized samples. Thus, for example a device can be used for blending conventional 5 ml to 80 ml samples and for much smaller samples. Moreover the provision of adjustment means, means that it is a simple matter for a user to change the spacing between the paddle and carrier support (change the paddle clearance) for different sized samples.
Typically, the adjustment means comprises a user operable control for use in varying the spacing. The user operable control may comprise a knob which is rotatable by the user to vary the spacing.
Preferably the adjustment means is arranged so that the spacing may be varied during operation of the device. This means that the process of blending a sample may be begun and the pressure exerted on the bag, and sample, changed during the blending process.
Preferably the adjustment means comprises a cam arrangement for varying the spacing between the extended paddle position and the carrier support.
Because of the continual operation of the paddles when the device is in use and the forces exerted between the paddles and the carrier support, the adjustment mechanism needs to be robust. For this reason a cam arrangement is favored over use of a lead screw or some other threaded component, which is more likely to wear or jam over time.
The cam arrangement may comprise a pair of interacting cam portions whose cam surfaces face one another. A first of the cam portions may be mounted against rotation in the device and a second of the cam portions may be mounted in the device for rotation relative to the first cam portion. The cam portions may be arranged so that relative rotation of the pair of cam portions causes a spacing between their respective mounting points to change.
The second cam portion may be rotatable by rotation of the user operable control.
The device may comprise a backing portion on which the carrier support is mounted. The carrier support may be arranged for movement relative to the backing portion to change the spacing between the paddle when in its extended position and the carrier support. One of the cam portions may be mounted on the carrier support and the other of the cam portions may be mounted on the backing portion such that relative rotation of the cam portions causes the spacing between the carrier support and the backing portion to change, thus changing the spacing between the paddle when in its extended position and the carrier support.
Preferably the device comprises a door which comprises the backing portion, the carrier support and the adjustment means. The backing portion may comprise the outer surface of the door. The user operable control may be provided at the outer surface of the door.
Where the user operable control is a knob this may be mounted to the second cam portion and protrude through the backing portion. Thus in the case where the backing portion comprises the outer surface of the door, the knob for adjusting the paddle clearance may be provided on the door.
According to a second aspect of the present invention there is provided a sample bag comprising a generally triangular sample holding portion.
The generally triangular shape of the sample holding portion allows easier collection of the sample after blending. When the blending process is complete, a user may grasp the bag and, using his thumb and forefinger (or otherwise), drag the dispersed sample to an apex of the triangle. Once the sample has been collected in an apex of the triangle, a pipette tip may be inserted into the bag to collect the sample from the corner. This method results in minimal loss of sample.
Here what is important is that there is a collecting zone for the sample. Thus the expression generally triangular should be interpreted broadly, for example, the triangle could have curved sides.
According to another aspect of the present invention there is provided a sample bag comprising a sample holding portion that comprises a sample collecting portion. The sample collecting portion should preferably be small compared to the size of the bag.
According to yet another aspect of the present invention there is provided a sample bag comprising a sample holding portion and sealing means for sealing the sample holding portion until use.
The sealing means may comprise a closure portion that may be removed to allow access to the sample holding portion.
The sample bag may comprise a pair of generally rectangular sheets which may be sealed together by a pair of seal lines to form the generally triangular sample holding portion.
There may be further seal lines between the pair of sheets, although often such additional lines will serve no useful function.
A seal line may be provided to seal the sample holding portion until use. Said seal line may be provided between the pair of seal lines forming the generally triangular sample holding portion, so forming a triangular sample receiving portion sealed against the ingress of material. Said seal line may be provided in a closure portion.
To use the bag, the user may tear or cut the closure portion away from the remainder of the bag to allow access to be obtained to the interior of the sample holding portion.
One or more seal line may be applied to a generally rectangular bag to form the sample holding portion, and a further seal line may be applied to seal the sample holding portion until use.
The sample bag may be a paddle blender sample bag.
According to a third aspect of the present invention there is provided a method of preparing a sample comprising the steps of:                a. placing material in a sample bag comprising a generally triangular sample holding portion;        b. blending the material; and        c. extracting a sample from the bag by squeezing the bag to cause at least some of the contents to collect in an apex of the generally triangular sample holding portion and extracting the collected contents from the apex of the sample holding portion.        
According to a fourth aspect of the invention there is provided apparatus comprising a device according to the first aspect of the present invention and a bag according to the second aspect of the present invention wherein the width of the bag is substantially the same as the width of a paddle in the device which is arranged to contact the bag for blending of the contents.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.